Maou

Maou

A high-level demon, he had three hearts before giving one to Nanoha. All three must be destroyed in order for him to die.
Despite his power, he often has a very childish personality and is gluttonous. Often taking the form of a little boy, some of his actions in this form disturb Nanoha such as when he reads porn, smokes, and drinks beer.
Despite his constant vow to retrieve his heart from Nahoha, his determination becomes weaker and he comes to deeply care for her.
He even gives her another of his hearts when the first is taken by an enemy.